Japanese patent laid open publication No. 2002-364317 filed by the assignee of the present application discloses a device for varying the lift of the intake valves of an internal combustion engine in a continuous manner. In this device, a worm connected to an output shaft of an electric motor meshes with a sector worm wheel which in turn rotates a lever directly connected thereto. The lever is configured in such a manner that the transmission ratio of the cam lift to the valve lift is varied in dependence on the angular position of the lever. This allows the valve lift to be varied in a continuous manner, but does not allow the opening timing of the valves to be varied. Therefore, when the valve lift is reduced in a low-speed, low-load state, the intake valves remain substantially closed in an early stage of each intake stroke of the piston and this undesirably increases a pumping loss in the intake stroke.
To enable the timing of the intake valves to be varied also, Japanese patent laid open publication No. 2003-003811 discloses the use of a camshaft including a cam whose profile varies in the axial direction and an actuating device that can selectively move the camshaft in the axial direction. This allows both the lift and timing of the engine valve to be varied in a continuous and smooth manner particularly if a ball spline or roller spline is used for the sliding surface of the cam.
However, as this prior proposal depends on a highly complex cam profile for achieving a desired valve timing and lift, a considerable expense is required to manufacture such a camshaft. Also, a drive mechanism for moving the cam is required to be provided in association with the camshaft, and this also adds to the complexity and manufacturing cost of the valve actuating device.